WHITE PAPERINTERCEPTINGINTERFERENCECAMBIUM’S INDUSTRY LEADING WIRELESS BROADBAND EXPERTISEHELPS TO SUBSTANTIALLY REDUCE THE EFFECTS OF INTERFERENCEFOR POINT-TO-MULTIPOINT WIRELESS ACCESS AND DISTRIBUTIONNETWORKS IN BOTH LICENSED AND UNLICENSED FREQUENCIES.
Wireless broadband has emerged as the most cost-effective technology for delivering high-speed Internet access to residential and business users, especially those in outlying and low-density environments. In the minds of many, the major challenge for wireless network providers is making sure of their equipment’s ability to overcome the effects of interference to deliver service with both high performance and high reliability. It’s a fact that wireless systems, whether operating in licensed or unlicensed frequencies, must cope with interference that can disrupt signals and cause transmission delays caused by errors. But it’s also a fact that if a wireless system is designed and built from the ground up to operate in the presence of interference, it can deliver consistently reliable performance and connectivity, enhanced customer satisfaction and excellent ROI. At Cambium Networks, our RF expertise, experience in outdoor communications, and technology leadership help us design fixed wireless networks that tolerate outdoor interference more successfully than any other wireless broadband solution available. Among the numerous features that make Cambium Networks successful at mitigating outdoor interference, two stand out. The first is the Cambium Air Interface Protocol, the fundamental system element that helps neutralize interference from external sources including ambient noise and interference from signals from other emitters and devices using the same frequency. The second is the fact that Cambium’s entire Point-to-Multipoint (PMP) technology portfolio offers GPS synchronization to limit the network’s own self-interference. Cambium provides proven PMP wireless network solutions for fixed outdoor networks in licensed or unlicensed bands and in line-of-sight (LOS), near-line of sight (nLOS) and Non Line of Sight (NLOS) environments. Most important, Cambium’s wireless solutions can be fitted exactly to your specific requirements and business case.SOLUTION PAPER INTERCEPTING INTERFERENCE 2
INTERFERENCE AND RELIABILITYWhat exactly is interference and why is it such a problem? INTERFERENCE INTERPRETEDIn the unlicensed wireless environment, interference can What are the most common types of interference and howbe defined as unwanted, competing radio signals in the do they differ from one another? In general, there are threesame frequency band. These interfering signals can disrupt, basic categories of interference:delay and reduce the reliability and quality of your networktraffic and performance. In licensed frequency bands SELF-INTERFERENCE. Emanating from anwhere no outside signals are competing, the issue is organization’s own operating environment, self-interferenceself-interference, i.e., your own network’s signals is a factor in both licensed and unlicensed frequencies. Incompeting with each other. In either case, the results either band, self-interference occurs when distinct signalsgo beyond lower quality transmission; they extend to come from a network under your control, whether fromcustomer dissatisfaction, loss of competitive advantage the same tower location or from several miles away. “ e’ve always liked the Wand decreased return on investment. Furthermore, the larger and denser the network grows, Cambium equipment the more it will be exposed to self-interference and theEXCLUSIVITY AND reliability and performance issues it may cause. because of its signal-FREE USE OF SPECTRUM to-noise ratio andBasically there are two types of frequency bands in which How do you limit self-interference? In most cases, it is best the fact that it alwayswireless networks operate: the licensed and unlicensed dealt with in the network planning stage. In building or performs well in verybands. Characteristics of each include: extending a wireless network, proper product design, ad- vanced technology (such as Cambium’s industry leading use noisy environments.” of GPS synchronization) and the ability to reuse a frequency Tim ChandlerLICENSED FREQUENCIES. Licensed frequencies band within the spectrum can in most cases combine to Presidentare bands reserved for the exclusive use of a public/private reduce self-interference to a point at which it does not have CoastalCOMSentity. Since the spectrum is clean and clear with no RFemitters (controlled by other entities) operating in the same a significant impact on network performance and reliability.frequency, wireless system reliability is greatly improved.Interference issues are largely confined to self-interference EXTERNAL INTERFERENCE. In unlicensedproblems. frequencies, interference is more difficult to manage, since the interference comes from networks and technology notUNLICENSED FREQUENCIES. Frequently described under your control. Because a single access point canas a “Free Use” environment, unlicensed frequencies support hundreds of subscribers or end users, interferenceprovide spectrum that is available to virtually anyone can have a substantial impact.that wants to use it. Signals from different transmitting Other networks aren’t the only culprits; more and moreorganizations and entities may compete with one another network interference is coming from a wide range offor space, creating an environment in which interference consumer devices — such as surveillance cameras, Wi-Fiand ambient noise — as well as self-interference — can hotspots, and microwave ovens — that may operatebe significant impairments to reliable communications. in or near the same frequency. The truth is, a simple babyThe sheer number of the competing signals in unlicensed monitor positioned too close to an access point canspectrum places a premium on ensuring that the equipment cause service disruption over 20 or more square miles.you use is of exceptionally high quality and design. Furthermore, a network must be designed to not only deal with present interference sources, but must also be pre- pared to deal with potential future sources as the wireless environment evolves and usage of the spectrum expands. AMBIENT NOISE. Also called the noise floor, ambient noise is simply background noise that is always present in a frequency band. It is caused by the growing numbers of wireless devices — from garage door openers to other wireless networks — operating in the same unlicensed frequency. These all crowd the spectrum and can be a significant factor in degrading signal and bandwidth. Ambient noise levels increase as more devices and networks are deployed in the spectrum.SOLUTION PAPER INTERCEPTING INTERFERENCE 3
NEUTRALIZING INTERFERENCEIn the world of outdoor wireless broadband networking, thousands — to transmit at the same time and alter-interference is a fact of life. Much as you’d like to, you natively receive as all of the subscriber modules in thecan’t eliminate it or simply make it disappear. What you network transmit at the same time in turn. This helpscan do, however, is neutralize it. You can make sure it prevent radio signals transmitted by an access point “We use the Cambiumdoesn’t disrupt your network operations or your end users’ transceiver to interfere with reception of a user signal PMP solution becauseperformance and satisfaction. That’s what’s important. As by another access point transceiver, perhaps the most we’ve found it to bea wireless pioneer, with more outdoor wireless experience onerous kind of self-interference in time-division duplexthan any manufacturer, Cambium Networks knows more radio networks. With GPS synchronization, you can be the most resilientabout mitigating the effects of interference than virtually certain your network can scale and grow elegantly to connection in our typeanyone. Our PMP networks, and our entire wireless serve increasing numbers of users and applications. of urban businessportfolio of products, are designed from the ground up to environment. Theensure that the effects of interference will not adversely • CAMBIUM AIR INTERFACE PROTOCOL. As solution keeps theaffect your network connectivity or performance, your end mentioned previously, for the most effective interference signal strength high,user satisfaction or your return on investment. Cambium’s mitigation, it is crucial to have a network designed to even with rain andunique interference-neutralizing solutions include: prevent or reduce unwanted signals. This begins with interference, providing the design approach taken in the Media Access Control C/I ratios that allow us• GPS SYNCHRONIZATION. Cambium leads the (MAC) layer. Unlike many other systems, Cambium to deliver 100 percent wireless industry in its usage of powerful GPS synchroni- designs its MAC frame to carry radio data packets throughput.” zation capabilities in all its PMP networks. This valuable (RDP) of a relatively small size. If and when interference capability dramatically reduces self-interference in both corrupts reception of an RDP, the small size means that Shane Hampton licensed or unlicensed frequency bands. GPS synchroni- retransmission of RDPs is kept to a minimum, assuring Business Only Broadband zation allows all sites to be set to the exact same clock a negligible impact on overall network throughput. so network timing is very precise. As shown in the diagram, Cambium’s PMP equipment also incorporates centralized GPS satellite timing signals reach the GPS receivers in request-grant transmission control that reduces demand each of the network’s access point radios establishing contention and allows SMs to transmit data only when a common timing reference. This allows all the access permitted by the access point, reducing data packet point radios in the network — whether hundreds or corruption and retransmission and maximizing throughput. GPS SYNCHRONIZATION EQUIPMENT KEY: POINT-TO-MULTIPOINT ACCESS POINT CLUSTER & CLUSTER MANAGEMENT MODULE GPS ANTENNA POINT-TO-MULTIPOINT SUBSCRIBER MODULESOLUTION PAPER INTERCEPTING INTERFERENCE 4
CARRIER-TO-INTERFERENCE RATIO LEFT: POOR COVERAGE IN AN UNSYNCHRONIZED DENSE DEPLOYMENT DUE TO HIGH INTERFERENCE RIGHT: PMP COVERAGE IN A SYNCHRONIZED DENSE DEPLOYMENT – LARGE AREA OF GOOD COVERAGE WITH LITTLESELF INTERFERENCE LEVELS “We found that the carrier-to-interference ratio on the Cambium system is so small that the system can operate with substantialCambium PMP networks also reduce interference in many effects of interference from signals in the interference and stillother ways, including: neighboring frequencies, thus improving reliability maintain higher-quality of communications. of service than• DIRECTIONAL ANTENNAS. Antennas focus RF alternative equipment. transmissions and eliminate susceptibility to signals • CARRIER-TO-INTERFERENCE RATIO (C/I) Even in congested from outside of the transmission area. Cambium PMP RATIO. The C/I ratio measures signal strength versus bands, the Cambium products use directional antennas to focus and narrow interference strength. The lower the C/I ratio, the more the signal beamwidths to make them more efficient, difficult it is to distinguish the desired incoming signals equipment gives us strengthening the main signal while minimizing side from the interference. Cambium PMP networks are great penetration in the and rear signal leakage and reducing interference to known for their exceptional ability to decode incoming high foliage areas and other transmissions. This reduces the noise floor from signals and maximize performance in low C/I mitigates interference unwanted transmissions including emissions from other environments. Because of their unique design, Cambium amazingly well.” devices and networks in the spectrum. radios need a minimum amount of signal above the Mark Novey interfering signal to operate successfully, as shown Director of Information• NOISE FILTERS. Cambium PMP networks also in the diagram. The result is, in many situations, Technology provide leading edge noise filters that help reduce the Cambium radios will work where other radios cannot. TelpageSOLUTION PAPER INTERCEPTING INTERFERENCE 5